Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

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Is there a true parallel between Gibbs' phase rule and Euler's polyhedral formula?

Gibbs' phase rule states: $$F=C-P+2$$ where $F$ is number of degrees of freedom, $C$ is number of components, $P$ is number of phases. Euler's polyhedral formula states: $$V+F-E=2$$ where $V$ is ...
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451 views

Mechanical Equivalent of Heat

Recently I have been looking up James Joule's experiment regarding the mechanical equivalent of heat. After viewing some drawings of the apparatus, I assumed that the lines holding the weights would ...
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Should I heat my room when I'm not here, energy-efficiently speaking?

I was wondering as it's getting cold : is it better for my electricity bill to shut down completely my (electric) heater during day, and to turn it on again when I come home (then it will have to heat ...
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Why isn't the Earth's core temperature the average of its surface temperatures?

Assuming that the earth is spherical, that its temperature is continuous, and that some other more or less realistic conditions hold, we might think that the Earth's core temperature should be about ...
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Why do lightbulbs continue to glow after the light is turned off?

I've noticed that whenever I turn the lamp off in my room at night, the lightbulb seems to continue to glow for a minute or so after that. It's not bright though; the only way I even notice it is if ...
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Why isn't water running faster hotter?

I was running the washing up water this morning, and started to think about why the cold tap isn't hot, and why the water doesn't get hotter the faster it is flowing (if anything, the cold tap gets ...
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271 views

Physical interpretation of changing variables $S(T,V)$ to $S(T,p)$

I'm confused in this situation. In an example of this book (Example 16.5. Thermal Physics, by Blundell) they ask to prove that $$C_P - C_V = VT\frac{\alpha^2}{\beta_T}\tag{1}$$ but using the fact ...
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Can I take heat from the air and convert it to electricity?

Its a summer day and the air in my house has been heated up. I could switch on my air conditioning, but then I'd be using energy from the grid in order to reduce the amount of energy in my house. ...
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How is thermodynamic entropy defined? What is its relationship to information entropy?

I read that thermodynamic entropy is a measure of the number of microenergy states. What is the derivation for $S=k\log N$, where $k$ is Boltzmann constant, $N$ number of microenergy states. How is ...
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Chemical potential of particles with zero mass

Why massless particles have zero chemical potential?
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873 views

How does cold air move through a room

If you turn on a fan in a warm room, it feels as if cold air is being pushed from the fan out in the direction that it's facing, but what's actually happening on a molecular level? When an object is ...
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637 views

What is the meaning of following expresion $C=\frac{\delta Q}{dT}$ mathematicly

Our professor raised the following question during our lecture in Statistical Physics (even so it's related to Thermodynamics): Many text books (even wikipedia) writes wrong expressions (from ...
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Why does microwaved food get cold faster

My evidence is entirely anectodal and non-scientific, but I've noticed food gets cold faster when it's been heated in a microwave instead of a stove. Is this true? And if it is, why does it happen?
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After what speed air friction starts to heat up an object?

I understand that air friction cools off an object at low speeds. For example, if you blow on a spoon of hot soup, it cools off. Or if you swing a hot frying pan in the air, it cools off faster. But ...
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Why did my liquid soda freeze once I pulled it out of the fridge?

Can someone explain in both layman's terms and also technically why when I pulled my glass filled with liquid soda from the freezer, the liquid soda quickly froze? Doesn't this violate the 2nd law of ...
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How does the temperature of the triple point of water depend on gravitational acceleration?

Suppose I do two experiments to find the triple point of water, one in zero-g and one on Earth. On Earth, water in the liquid or solid phase has less gravitational potential per unit mass than water ...
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768 views

Second Law of Thermodynamics and the Arrow of Time: Why isn't time considered fundamental?

I've come across this explanation that the "arrow of time" is a consequence of the second law of thermodynamics, which says that the entropy of an isolated system is always increasing. The argument is ...
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459 views

How is this process not quasi-static yet reversible?

Consider a (adiabatic) canister with a piston containing some gas kept in a vacuum. There are two weights on the canister which equalize the pressure of the gas on the piston. Assume the system is at ...
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Is energy the ability to do work?

Here was my argument against this, the second law of thermodynamics, in effect says that, there is no heat engine that can take all of some energy that was transferred to it by heat and do work on ...
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373 views
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Hot water freezing faster than cold water

This question has puzzled me for a long time. There is already a question like this on Physics.SE. John's answer to the question seems quite satisfying. But when I googled the cause I found this and ...
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410 views

Is temperature quantized?

I'm learning quantum mechanics on my own. I've known that energy is quantized and I've started wondering about temperature. From thermodynamics we have: $$U=\frac{3}{2}NkT $$ (for ideal gas, of ...
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Is there a number that describes a gas's departure from the ideal gas law?

When judging if relativity is important in a given phenomenon, we might examine the number $v/c$, with $v$ a typical velocity of the object. If this number is near one, relativity is important. In ...
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417 views

Why does a short circuit generate fire?

When a short circuit occurs it's obvious that there is fire. How come electric energy turns out to be heat energy? What causes the conductors to get hot when short circuit is present.
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201 views

Measuring temperature at a distance

http://www.youtube.com/watch?v=gKYrXHZwtPw In this video it is explained that Land Skin Temperature (LST) are measured by NASA's Aqua and Terra satellites. It seems it works by collecting the ...
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Clear up confusion about the meaning of entropy

So I though, and was told, that entropy is the amount of disorder in a system. Specifically the example of heat flow and it flows to maximize entropy. To me this seemed odd. This seemed more ordered ...
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555 views

Can a single molecule have a temperature?

A show on the weather channel said that as a water molecule ascends in the atmosphere it cools. Does it make sense to talk about the temperature of a single molecule?
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Maxwell's Demon Constant (Information-Energy equivalence)

New Scientist article: Summon a 'demon' to turn information into energy The speed of light c converts between space and time and also appears in e=mc^2. Maxwell's Demon can turn information supplied ...
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Is “detailed balance” equivalent with a continuity equation in state space?

I have a talk tomorrow in which detailed balance is needed and I don't want to bore my audience with elaborate explanations for it so I'm looking for simpler explanations. As far as I understood it ...
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Physical interpretation of different boundary conditions for heat equation

When solving the heat equation, $$ \partial_t u -\Delta u = f \text{ on } \Omega $$ what physical situations are represented by the following boundary conditions (on $\partial \Omega$)? $u=g$ ...
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How does an earthen pot keep water cool?

I understand that evaporative cooling takes place thanks to small pores contained in the pot and that allow some water to go through and evaporate. However I couldn't understand clearly whether water ...
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411 views

Confusion regarding entropy, reference papers request

1.a In paragraph at Wikipedia/Entropy it is stated: This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy ...
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Why is air a poor conductor of heat?

Today, I was reading an article How Thermoses Work It goes on to explain all three processes of heat transfer: Conduction Radiation Convection In Convection, It states, If it weren't for ...
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Is there a relativistic generalization of the Maxwell-Boltzmann velocity distribution?

The Maxwell-Boltzmann velocity distribution in 3D space is $$ f(v)dv = 4\pi \left(\frac{m}{2\pi k_B T}\right)^{3/2} v^2 \exp\left(-\frac{m v^2}{2k_B T}\right)dv$$ It gives the probability for a ...
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Are there materials that get softer with temperature decrease?

Could be there material that begins melting/softening when it's temperature is lowered? I would say no, but I've seen enough physics to know that not always life is so easy. Moreover I think I've ...
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197 views

Why does Joule heating not occur when no current flows through a conductor?

Joule heating happens every time when the conduction electrons transfer kinetic energy to the conductor's atoms through collisions, causing these conductor's atoms to increase their kinetic and ...
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293 views

How can I determine the coefficient $k$ in $ \dfrac{dT}{dt} = -k(T - 100 \mathrm{^\circ C}) $?

I recently spend some time on cooking and I'm curious about the time evolution of the temperature of the water. I did some experiment and the temperature is of the form $$ T = 100 \mathrm{^\circ C} + ...
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What pressure or tension occurs in a glass jar when I pour boiling water inside?

Sometimes it happens that when you pour a boiling water into a glass jar, it cracks. Since glass is very hard material and resilient to pressure, the tension must be very high. Is it possible to ...
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597 views

Why does blowing on someone who is wet feel colder than on someone who is dry?

The title says it all. If I'm standing in the wind and I'm wet, I feel much colder than when I'm dry. This is true no matter how warm or cold the water. Why is this?
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Minimal temperature achievable by vanilla Peltier element?

I wonder, are there any fundamental issues leading to reduced performance of Peltier elements at cryogenic temperatures (-100C and lower)? What is theoretical/practical minimum temperature ...
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554 views

Why do moving particles emit thermal radiation?

While answering another question about heat in an atom, the discussion in the comments led to the question of how heat is related to thermal radiation picked up by infrared cameras. The answer is that ...
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848 views

Why are the virial coefficients functions of temperature only?

I have read in multiple places that the virial coefficients in the virial equation of state, $Z=1+{B \over v}+{C \over v^2}...$, are functions of temperature only and are independent of pressure (or ...
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579 views

Can a water bubble be frozen into ice bubble?

To maintain the surface tension which formed our original bubble (in order to keep the bubble from breaking), we may change the temperature/pressure of air on both sides of the bubble varyingly, with ...
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282 views

Radiation– white vs black house, hot or cool?

In my book's thermodynamics chapter, it says that an "object that radiates heat faster also absorbs heat faster. This means that an object that is a more efficient radiator comes to equilibrium ...
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217 views

How to derive a physical model of temperature above the earth surface?

At a point on the surface of the Earth, if I go straight "up" a distance $z$ (radially outward from the Earth), I'd observe a temperature profile $T(z)$. The conventional wisdom from the meteorology ...
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345 views

Gas kinetic representation of trans-critical conditions

From a molecular point of view, can we think of the super-critical conditions as conditions where T and p are large enough that the collisions of gas molecules are frequent and powerful enough to ...
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Recommendations for Statistical Mechanics book

I saw Book recommendations No reference to Statistical Mechanics there. I learned thermodynamics and the basics of statistical mechanics but I'd like to sit through a good advanced book/books. Mainly ...
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How much energy from extreme coldness?

Let's say I have: 1: one mole of extremely cold ideal gas 2: unlimited amount of ideal gas at temperature 300 K 3: one ideal heat engine Can I generate for example 1 MWh of mechanical energy using ...
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Bulk flow of air in a long tube between Antarctica and Australia?

I have a 5km diameter clear plastic tube which is open at each end and runs from the center of Antarctica to Lake Eyre in Australia. The tube is on the ground where it can be and at sea level on the ...
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468 views

Is there a formal definition of a macroscopic variable in statistical mechanics?

Intuitively it's easy to accept that the usual variables like temperature, internal energy, etc. are 'macroscopic', but does there exist a formal definition of a macroscopic variable? In other ...